The present invention relates to end-to-end assembly of two parts that overlap via respective edge portions, the parts being made of materials having respective different coefficients of expansion.
A field of application of the invention lies in assembling together parts in subassemblies of gas turbines, in particular aviation gas turbines, and more particularly, but not exclusively, to two parts made respectively of a metal and of a ceramic matrix composite (CMC) material. Examples of such assemblies are an assembly constituted by an upstream secondary nozzle and a downstream secondary nozzle in an aeroengine, or an assembly formed by an end wall and an inner wall or an outer wall in a gas turbine combustion chamber.
In order to assemble together parts made of materials having significantly different coefficients of expansion, it is known to make use of connections that are flexible and capable of deforming elastically to absorb the differences between dimensional variations. Thus, it is known to use flexible connections for connecting CMC combustion chamber walls together with metal casings in a gas turbine. Reference can be made in particular to document US 2006/0032237.
FIG. 1 is a fragmentary and diagrammatic view showing the use of such connections for assembling a metal upstream secondary nozzle 1 with a CMC downstream secondary nozzle 2 at the outlet from a gas turbine aeroengine (where the terms “upstream” and “downstream” are used herein with reference to the flow direction of the gas stream through the engine).
The flexible connections are embodied by metal connection tabs 3 that are curved so as to be elastically deformable. At one end, each connection tab 3 is fastened, e.g. by bolting, to a flange 4 forming part of the upstream secondary nozzle 1, in the vicinity of its downstream end edge. At its other end, each tab 3 is fastened, e.g. by bolting, to the wall of the downstream secondary nozzle 2 in the vicinity of its upstream end edge. Since clearance is present between the adjacent annular edge portions of the nozzles 1 and 2, sealing is provided by a sealing device 5 such as a split metal gasket with petals that is fastened to the downstream end of the nozzle 1.
The use of connection tabs involves a certain amount of handling and adjustment during assembly. In addition, the presence of the connection tabs and of a flange, and the need for a sealing device give rise to an increase in weight and in production costs.